path ops : add support for inverse fill

add inverse fill, reverse diff, and gm tests
cleaned up some interfaces
Review URL: https://codereview.chromium.org/14371011

git-svn-id: http://skia.googlecode.com/svn/trunk/include@8798 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed